Engineering Intermolecular Charge Transfer in Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Generation

Intermolecular charge transfer (ICT) plays a vital role in photocatalysis, particularly in donor-acceptor systems. In these regards, covalent organic frameworks (COFs) have recently attracted attention due to the ease with which their electron donor-acceptor building blocks can be adjusted to influence their structure-activity relationships. Therefore, a thorough investigation of charge transfer across the photocatalyst framework is essential to achieve highly effective and unprecedented photocatalytic performance. Here, we present a series of donor-acceptor COFs with gradually increasing acceptor strength in their constituent moieties, and examine the impact of this on the photosynthesis of hydrogen peroxide (H2O2), a versatile green oxidant. Of the materials in this series, TTT-DTDA COF exhibited optimal intermolecular charge transfer efficiency and demonstrated a maximum H2O2 yield of 1,265 µmol g-1 h-1 in pure water and in the presence of natural air. Photocatalytic H2O2 generation in the biphasic benzyl alcohol/water system reached 21,541 µmol g-1 h-1, which exceeds the performance of most reported photocatalysts. Thorough experimental and theoretical investigations have been conducted to study this phenomenon and to explore the potential of metal-free COFs as photocatalysts for photocatalytic H2O2 generation.